Disposable diapers are composite absorbent articles that are designed to be worn about the lower torso as undergarments by incontinent persons and by infants and young children prior to toilet training. Disposable diapers typically include a liquid impervious back sheet as the outer surface of the diaper, a liquid pervious topsheet as the inner surface of the diaper for placing adjacent the skin of the wearer, and an absorbent core placed between the topsheet and the back sheet for absorbing urine and other liquids. The absorbent core is normally contained in a central, longitudinally extending region of the diaper and the topsheet and back sheet are normally bonded about the periphery of the diaper.
The diaper is placed between the legs with the topsheet next to the skin and the ends are fastened at the waist to hold the diaper in place for the collection and retention of urine and feces. One area of concern in the development and construction of the modern disposable diaper has been maintaining the wearer's comfort and the fit of the diaper throughout the period of use of the diaper, especially on active infants and young children.
Disposable diapers have front and back waist regions that are usually characterized by side panels or ear flaps that extend in the lateral direction on each end of the diaper so as to encircle the waist and hold the diaper in place. The front waist region normally includes a landing member upon which decorative indicia may be placed. The back waist region normally includes a securing tab on each side for attaching to the landing member. The securing tab and landing member can be attached by hook and prong fastening means similar to Velcro, by a pressure-sensitive adhesive on a securing tab tape, or by other suitable means.
Disposable diapers may also include elasticized waist bands, leg cuffs and side panels. The elasticized components improve the fit of the diaper and can assist in precluding leakage from the diaper.
U.S. Pat. No. 5,242,436 is directed to a disposable diaper that has an elasticized waist band with a dual tensioning fastening system to improve the dynamic fit of the elasticized waist band and the containment characteristics of the absorbent article. A pair of elasticized side panels that are elastically extensible in the lateral direction are disposed in the back waist region between the topsheet and the back sheet in the ear flaps of the diaper on either side of the absorbent core.
The topsheet and the backsheet are extensible, but inelastic. The webs can be stretched, but are permanently elongated and do not have significant recovery of their prestretched dimension. It is necessary to activate the topsheet and back sheet in the region of the elastic side panels so that the topsheet and back sheet can stretch and recover with the side panels. The topsheet and back sheet are activated by incremental mechanical stretching in the cross-machine direction. A laminate of the topsheet, back sheet, and elastic side panel is passed in an untensioned condition through at least one set of meshing corrugated rolls. The laminate is rendered elastically extensible in the cross direction up to the limit of incremental stretching.
U.S. Pat. Nos. 4,981,747 and 5,114,781 are directed to the preparation of composite elastic laminates for use in disposable absorbent articles, including diapers. The laminates are of elastic materials and extendable but nonelastic nonwoven webs. The webs are described as “reversibly necked,” which is to say that the webs are permanently elongated in one direction and necked down in a direction generally perpendicular to the direction of elongation of the web. The web is heat treated while necked. The heat treatment is said to impart memory to the nonelastic webs so that the webs can then be stretched and recover in a direction generally parallel to the direction of neckdown and perpendicular to the direction of elongation. Extension of the reversibly necked material is described as limited to the pre-necked dimensions.
A composite elastic laminate can be prepared by laminating the reversibly necked material to an elastic material. The laminate is said to be elastic in a direction generally parallel to the direction of neckdown of the reversibly necked material. A laminate that is elastic in two directions can be prepared if the reversibly necked material is laminated to an elastic material elongated in the direction of extension of the web and then relaxed. The reversibly necked material is gathered between points of attachment to the elastic material and is said to have stretch and recovery to the extent the gathers allow the elastic material to elongate.
Hassenboehler, Jr. et al. U.S. Pat. No. 5,244,482 describes another method for drawing a web of nonelastic nonwoven fibers in the machine direction. The stretched web is said to be useful as a filter material and to have reduced pore size, improved uniformity in pore size, and high lateral elasticity characteristic of stretch fabric having approximately 120% elongation to break. The web is said to be useful in preparing laminates with webs of elastomeric polymers, among others.
The precursor web has substantial bonding and relatively low processing extensibility and is heated to its softening temperature and drawn in the machine direction. Elastomeric polymer webs and webs having 50% standardized elongation before break are said to be totally unsatisfactory for use in the practice of method.
It would be desirable to provide alternative composite elastic laminates that have improved properties, are more versatile, or require less effort to prepare. It would be desirable to develop nonwoven webs for composite elastic laminates that are strong enough to withstand the rigors of incremental mechanical stretching in diaper construction where it is desirable to use elastomeric strands or scrim for breathability, rather than films.